A click on the test Console's Resume button opened window.confirm and the
browser daemon hung: the mouse release, screenshots and the frame tree all
block until the dialog is answered, and ui-browser had no way to answer it.
A click that opens a dialog now returns {dialog:{type,message}}. The new
command `dialog accept|dismiss` answers it and records the type, message
and answer in the receipt. While a dialog is open other commands except
stop refuse (journaled), and no screenshot or URL check is attempted.
A real-Chromium confirm test covers accept, dismiss and the refusals.
jason.woltje